In the BAF it was common knowledge that certain people - even amongst the volumous white belt crowd (no coloured belts), would 'assume' control and try to teach you what to do when training. It was a real pain in the A to train with these people, even if they were better than you.

This sounds a lot like not just Aikido, not just MA, but life in general. I think it's just human nature. There are people like this in practically every crowd, regardless of the activity or avocation.